Nonwoven composite fabric manufacturing is the fastest and the most economical way of converting fibers to fabrics. Before discussing the importance of FR nonwoven composite fabrics for use in military and functional garment applications, it is important to outline the basics of the manufacturing of conventional woven fabrics presently used in the military garments to clearly distinguish the difference between the woven and nonwoven fabrics.
Yarn Formation: The manufacturing of conventional woven textile fabric that is presently used to make the military garments is a laborious and multi-step (over 15) process with very slow production speeds. The production of conventional textile fabrics from staple fibers begins with the opening of bales of compacted fibers, synthetic or natural, combing, and then carding, whereby the fibers are individualized and aligned, the web from the doffer of the card then combined to form a thick rope called sliver. Multiple strands of sliver are then processed on drawing frames to further align the fibers, blend, improve uniformity and reduce the sliver's diameter. The drawn sliver is then fed into a roving machine to produce roving with false twist to provide some integrity. The roving is then fed into the ring or rotor spinning machine to be spun into yarn. The smaller yarn packages from the spinning machines are placed onto a winder where they are transferred into larger spools. The yarns are then wound onto a warp beam to be woven into fabrics.
Woven Fabric Formation: The woven fabric from the loom consists of warp and weft yarns. The warp yarns run in the machine direction whereas the weft yarns run in the cross direction or perpendicular to the warp yarns. The warp beams supply the warp yarns by unwinding and the weft yarns are inserted by high-speed shuttle, air or water to complete the fabric design. The warp yarns themselves are subjected to a sizing treatment with starch to provide some stiffness and abrasion resistance to take them through the process of weaving. The sizing treatment is removed by scouring and bleaching after the fabric is made on the loom before the fabric can be dyed and finished. One of the limiting factors of woven fabrics, apart from being a multi-step process, is the very slow production speed, i.e. a few feet (1-2) per minute even on the most modern looms.
On the other hand, nonwoven composite fabrics, when properly designed and processed, offer both technical and economic advantages, especially in the area of functional apparel. From an economics standpoint, the production of nonwoven fabrics and their composites using spunlaid and carded webs is known to be more efficient than traditional textile processes, with many fewer steps (less than 5) and faster production rates with machine speeds over 100 feet per minute. From a technology standpoint, multiple layers of fibers with varying functionalities, such as water repellent or absorbent and fire retardant, can be incorporated to provide unique structures that are not possible to manufacture by traditional yarn spinning and weaving techniques.
Nonwoven Composite Fabric/Garment: Nonwoven composite fabrics based FR garments can be made suitable for use in a wide variety of military and other applications where the efficiency with which the garments/fabrics is manufactured provides a significant economic advantage for these fabrics versus traditional woven textiles. However, nonwoven fabrics, especially the FR chemical treated fabrics, have been unable to penetrate the functional and everyday wear garment markets because of commonly known disadvantages, such as poorer drape, aesthetics, stiffness, abrasion resistance, launderability, tear resistance, recovery after stretching, etc. when compared with woven FR fabrics. Many of the nonwoven processes are intended for creating disposable or non-durable articles, such as pillow covers, baby diapers, sanitary napkins, medical gowns etc. at faster production speeds and cheaper price. None of the currently available nonwoven technologies, when used alone, offer a durable fabric for apparel or garment end use application. The challenge has been to judiciously use several known bonding methods and finishing treatments, while using proper fiber blends, additive, finishing chemicals and fabric construction. Attempts have been made to develop nonwoven fabrics for everyday wear, such as shirts and pants, as referenced in U.S. Pat. No. 3,933,304, where a washable spunlaced nonwoven cloth containing binder chemicals has been disclosed. U.S. Pat. No. 3,988,343 discloses a nylon fabric treated with binder chemicals. U.S. Pat. No. 5,874,159 discloses a spunlaced fabric containing a net made of a polymer that melts at lower temperature than base fibers and bonds with the nonwoven layers and thus provides the necessary durability during the end use application. More recently, U.S. Patent Application No. 2003/0166369 A1 describes a durable nonwoven garment with elastic recovery where a carded web is hydroentangled and modified with very high levels of acrylic binder before being assembled into a garment. The absence of any of these materials from the prior art in the commercial marketplace for everyday wear is an indication that further improvement and enhancement are required with respect to the processing, finishing and assembling of nonwoven based materials for apparel usage, especially for durable fire resistant military garment applications.
Hydroentangled/Spunlaced Nonwovens: It is an established fact that the best nonwoven bonding technology that is available on a commercial basis today to create fabrics that somewhat mimic the properties of woven fabrics, is the hydroentangled or spunlaced nonwoven fabric technology. The entanglement and the twisting of the fibers that occur in the case of spunlace fabrics is somewhat similar to the twist in the yarns of the woven fabrics and thus, spunlace fabrics provide the best drape characteristics among the commercially available nonwoven fabrics. The use of the right type of nozzles, their length, design, diameter and number of holes per jet strip, coupled with the position of the jet manifolds, the number of manifolds per side of the fabric and the water jet pressure critically impact the final fabric properties, especially the bonding of fibers and thus the strength and surface abrasion resistance. Even the spunlace nonwoven composites exhibit a higher degree of elongation or stretch than desired and poorer recovery from deformation. In addition, spunlace fabrics without any post thermal and chemical treatment show much poorer launderability and abrasion resistance compared to the woven fabrics. The loose end surface fibers need to be bound to the matrix of the fabric by thermal and/or chemical treatment techniques. Without these critical chemical treatments, the fabric is rendered useless just after a single laundering cycle.
The art of combining various nonwoven layers with and without support scrim through hydroentangling for multiple end use application is already established in the literature. Different nonwoven layers or webs, such as spunlaid or spunbonded, carded, wet-laid and needle-punched, can be combined with and without reinforcing scrim or nonwovens as referenced in U.S. Pat. Nos. 5,240,764, 5,334,446, 5,587,225, 6,669,799, 6,735,832 B1, and U.S. Patent Application No. 2005/0022321 A1 to provide unique composite structures for various end use applications. U.S. Patent Application No. 2004/0016091 by Rivera et al. discloses a method of forming a two-sided, nonwoven composite intended for use in durable three-dimensional imaged surfaces that is resistant to washing. The composite of the Rivera et al. application has been designed for applications other than functional apparel, as the fibrous and scrim elements incorporated in the application do not withstand the rigors of the military and outdoor end use. In addition, according to the Rivera et al. application, the fiber layers are separated by the scrim to avoid intermixing of the layers, which leads to delamination and failure of the composite based garment. The current invention addresses the need for intimate bonding, additional down-stream FR and binder chemical treatment to “lock” the twisted configuration of fibers for enhancing the abrasion resistance and wash durability.
Carded Precursor Webs: The carded precursor nonwoven webs contain staple or cut fibers used as the individual layers of the final bonded spunlace nonwoven composite fabric. It is possible to use synthetic fibers such as polyester, or nylon in blends with natural fibers, such as cotton, and regenerated fibers, such as rayon and cellulose acetate or blends of both types of fibers. For carded webs, the useful fiber denier ranges from 1-6 dpf and the fiber length ranges from 0.5-3 inches. Basis weight of the fabric ranges from 0.5 oz/yd2 to 6 oz/yd2. The fabric properties are determined by the optimization of fiber denier, length and construction. The compacted fibers from the bales are fed into various pre-opening and blending stations before being fed to the licker-in roll of the carding machine. The difference in surface velocity between the main cylinder and the numerous worker rolls or flat circulating wire strip located above the main cylinder is the reason for the thorough opening, individualization and parallel alignment of fiber web. The web can be cross-laid at a 45-degree angle using multiple layers to provide balanced properties in the machine and cross direction. The web integrity is possible only by bonding employing thermal calendering, needle punching or spunlacing techniques.
Military Uniform Garments: To date, the use of nonwovens in the military sector has been restricted mostly for special and niche applications, such as disposable apparel and shoe interlinings, due to limitations in performance. The FR military garments made using FR nonwoven composites of the current invention have the potential to offer relief from heat stress combined with better economics. However, the military applications require functional garments with specific performance attributes. The functional properties of current woven uniforms are fixed or limited by the properties of the individual yarns that lie in a two-dimensional plane. The three-dimensional, nonwoven, composite, fabric offers numerous possibilities of utilizing various fibers and fiber blends in multiple webs or layers and additive chemical technologies to impart specific functional characteristics for the intended use.
Dyeing and Printing: The polyester based nonwovens are traditionally dyed using disperse dyes where heat is applied to open the fiber structure for mechanical incorporation of dye molecules. In the case of nylon-based nonwovens, the fabrics can be dyed using acid, basic or vat dye molecules. Cellulosic fibers may also be dyed using the vat dyes. The vat dyes offer the best solution for color fastness and thus, durability of shade in end use. Deep shade is not a requirement for the military and outdoor garment fabrics; however, deep dyeing is possible with nylon-based garments.
Finishing Treatments: The finishing treatments consist of imparting abrasion resistance, wash durability, water repellency and fire resistance based on the needs of the end use application. The finishing treatments can be carried out using commonly known chemicals, such as phosphorous, silicone, acrylate, melamine, urethane, etc. using spraying, padding and curing or knife coating techniques commonly known in the industry. Spraying or padding intumescent fire retardant finishing chemicals can provide additional improvements in the fire resistance characteristics. Whatever the finishing treatment may be, care must be taken to avoid stiffening the fabric and reducing breathability and physical properties.